1. Field of the Invention
The present invention relates to a disk player in which reproduced data obtained by performing reproduction processing on a signal read from a disk, is stored in a buffer memory prior to a request for the data reproduction.
2. Description of the Related Art
Conventional disk players may play a disk which records computer data so that the disk is used as computer ROM for a host computer. CD-ROM drives are common examples of such apparatuses.
Such CD-ROM disk players comprise a buffer memory for the temporary storage of reproduced data read from a disk.
Data following the data requested by a host computer""s read command is sequentially read from a disk and reproduced in the same order as the data was recorded on the disk, prior to receipt of read commands for those data, and then cumulatively stored in the buffer memory.
When a sequential read command is issued, and it is confirmed that the requested reproduced data is data stored in the buffer memory, the requested reproduced data is transferred to the host computer. In this case, the command can be executed at a high speed because it is unnecessary to read data from a disk.
Here, in such CD-ROM players, the disk driving speed is generally set faster than the rated speed, and thereby the transfer bit rate for the reproduced data, i.e., the rate at which reproduced data is written into a buffer memory, is set faster than the reading rate at which reproduced data is read from the buffer memory.
In such disk players, in which the writing rate with respect to the buffer memory is set faster than the reading rate, it is possible to reread data from the disk when reproduced data can not be properly obtained, to achieve continuous output by taking advantage of the difference between the write and read rates with respect to the buffer memory.
In such disk players, when data must be read again from a disk due to, for example, the buffer memory overflowing or failed data reproduction, an access operation must be done to search for a needed signal and, until the access operation is completed, an optical head, a servo system circuit, and certain circuits in a read signal reproduction circuit system must operate, in which the optical head is necessary for an access operation, the servo system circuit is required for disk driving, and the certain circuits includes the circuits responsible for the processing until decoding of an address indicative of a reproduction position on the disk, in read signal reproduction processing. However, an error correction circuit, located downstream of the address decoding in the read data reproduction circuit system, need not operate at this point. Moreover, in the case of a CD-ROM player, a CD-ROM signal processing circuit, which carries out signal processing unique to CD-ROM data, also need not operate at this point.
Meanwhile when reproduction of a signal read from a disk is unnecessary because some data remain in the buffer memory, the data in the buffer memory may be read for output. In such a case, the optical head servo system circuit and a read signal reproduction circuit system need not operate.
In conventional disk players, such as is disclosed in JPA Hei 6-96520, a data reading means suspends operation when a buffer memory overflows, and remains at rest until the data in the buffer memory is reduced to within a predetermined level, to thereby save power consumption. Another similar power save type disk player is disclosed in JPA Hei 5-258460.
In the above conventional disk players, a reproduction circuit system, a spindle motor, an optical head, and a servo circuit are collectively handled as a single data reading means, wherein the reproduction circuit system reproduces the signals read from a disk to generate reproduced data, and the servo circuit controls the above circuits. That is, the operations of these circuits are controlled as a whole.
As a result, time is required to activate the spindle motor and bring disk rotation to a predetermined speed when the data reading means resumes operation. This delays the resumption of operation of the data reading means and subsequent data reproduction. This, in turn, leads to a problem such that a period in which the data reading means remains inoperative must be reduced.
In particular, with a disk player for a disk, such as a CD, with signals recorded according to a constant linear velocity method, rotation control cannot be achieved once reading of a recorded signal from the disk is stopped as rotation control is carried out using a signal read from the disk. This results in requiring an even longer time for data reproduction.
Here, when it comes necessary to reread signals from a disk, and an access operation is applied to determine a reading position on the disk, an address recorded in the disk must be demodulated. Presently, commercially available general disk players have a structure in which address demodulation is applied prior to error correction, which is one step in data reproduction.
Power consumption of an error correction circuitry section is generally relatively larger than that of other circuitry sections in a reproduction circuit system. In the above described disk players, an error correction circuitry section [a decoding section of a CIRC (Cross Interleave Read-Solomon Code)] is included in the data reading means, and therefore continues to operate during an access operation period in which data reproduction is not possible, while only consuming a negligible amount of power.
The present invention has been conceived to overcome the above problems and aims to provide a disk player which performs data reproduction, including read data correction, in synchronism with a bit clock, while controlling the rotation of a disk where signals are recorded according to a constant linear velocity method, using a constant angular velocity method. In this disk player, a rotation control circuit for carrying out rotation control for a disk, using a constant angular velocity method, is controlled independently of a head control circuit for controlling a head which reads a signal from a disk, such that the head is placed in a condition allowing signal reading from a disk, and a reproduction circuit system for reproducing the read signal to generate reproduced data to be stored in a buffer memory. Specifically, an operation suspend controller controls the operations of the head control circuit and the reproduction circuit system, but not that of the rotation control circuit.
With the above arrangement, in which the rotation of a disk with signals recorded in accordance with a constant linear velocity method is controlled using a constant angular velocity method, and the operation of the rotation control circuit is free from the control by the operation suspend controller so that the disk can continue to rotate, the disk can continue to rotate even while data writing to the buffer memory is stopped. Therefore, when signal reading from a disk is resumed, signal processing can promptly be performed to the read signals, regardless of the radial dimension of the reading position on the disk. This can reduce the transitional period to an access operation for reading a desired signal.
According to the present invention, the circuits involved in data reproduction processing, including error correction, with respect to the read data are controlled to suspend operation when writing to a buffer memory is halted, and to remain suspended until disk accessing begins again. During the period from beginning to completion of disk accessing, suspension of operation of the circuits responsible for data reproduction immediately before data correction is released, while the circuits responsible for data reproduction processing after data correction remain suspended.
With the above arrangement, in which circuitry sections irrelevant to data reading from the buffer memory are handled by a smaller unit, power consumption can be efficiently reduced.
According to another aspect of the present invention, when the operation suspend controller releases suspension of operation of the reproduction circuit system, the focus controller outputs a focus control signal indicative of a DC voltage level stored in a level storing section, so that, when signal reading is resumed, the light beam is focused in a condition similar to its average condition at a time when focus control was carried out, immediately before data reproduction was suspended. This allows smooth transition to a focus servo state and, as a consequence, smooth signal reading.
According to yet another aspect of the present invention, information on the last demodulated address is stored in the address demodulator, and, when re-reading from the disk is necessary, the stored information concerning the latest address is used in an access operation carried out with respect to the disk to determine a reading position on the disk.
Specifically, when the disk is accessed for rereading, while using the stored address information as a target address, a signal for a block which contains the data last written in the buffer memory, can be read again from the disk. In this manner, data can be reliably reproduced without the last data written being lost.
According to still another aspect of the present invention, when the amount of data in the buffer memory falls below a predetermined level, disk accessing is resumed to reread data from the disk. By controlling such that only reading from the buffer memory is performed until the data residual amount falls below a predetermined value, it is possible to supply additional data before the buffer memory is emptied. Thus, power consumption of the device can be easily reduced while maintaining maximum performance interms of data reproduction speed or other factors.